On 25/04/2017 00:13, Andras Szerdahelyi wrote:
I have a need to encode exception messages in to a specific JSON format in
my http responses. I was wondering how I could catch a
DeserializationException in my route or outside of it or encode the
DeserializationException.
Here's how I did it so that it integrasted into my existing REST service
error handling:
Wrapped the deserialization operation in a try block:
def getParam[T: JsonReader](params: MMap[String, JsValue], key:
String, delete: Boolean = true): T = {
val value = params.get(key) match {
case Some(v) => try {
v.convertTo[T]
} catch {
case de: DeserializationException => throw
deserializationToRESTException(de, key)
}
case None => throw RESTException(ERR_MISSING_ARG(key))
}
if (delete) params -= key
value
}
val restErrorRE: Regex = """^Expected (\w+) as \w+, but got (.+)$""".r
def deserializationToRESTException(de: DeserializationException, key:
String) = {
val msg = de.msg match {
case restErrorRE(t, v) => s"expected $key to be $t but got $v"
case _ => s"invalid value for $key"
}
RESTException(ERR_INVALID_ARG(msg), de)
}
Then I wrapped all the individual deserialization calls in a try block:
try {
:
val name = getParam[String](fields, "name")
val uid = getParam[Int](fields, "uid")
:
} catch {
case re: RESTException => complete(re.toResponse)
final case class RESTException(error: RESTError, cause: Throwable =
null) extends Exception(error.toString, cause) {
def toResponse: HttpResponse = error.toResponse
}
final case class ERR_INVALID_ARG(det: String = null)
extends RESTErrorWithDetail(400, "invalid input argument", det)
RESTErrorWithDetail just maps the error code and message onto a normal
HttpResponse containing the HTTP status code and a JSON formatted error
message:
override def toResponse: HttpResponse = {
if (detail != null) {
HttpResponse(status = code, entity =
HttpEntity(MediaTypes.`application/json`,
"""{ "fault": { "code": %d, "name": %s, "message": %s }
}""".format(
code, name.toJson, s"$msg ($detail)".toJson)))
} else {
super.toResponse
}
}
That way the JSON deserialization errors are handled as normal
completions rather than using a specific Akka-HTTP exception handler.
--
Alan Burlison
--
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